The present invention relates to a device for limiting the power output of a hydraulic assembly comprising plural hydraulic driven motors, hydraulic pumps for driving said driven motors, a pump driving motor and control means controlling the hydraulic flow from each pump to the driven hydraulic motor or motors coupled therewith.
In a hydraulic assembly of the above-mentioned type, the pumps of the driven hydraulic motors are coupled with the output shaft of the driving motor via a gearbox, and if the hydraulic power output exceeds the available power output of the driving motor, the latter will be overloaded, resulting in a decrease of speed or even a full stop of the driving motor. If the driving motor is an electric motor, the full stop may result in the destruction of the motor. For this reason, the pumps have to be so dimensioned that their combined maximum power does not exceed that of the driving motor, even if it is only in exceptional cases that all pumps are run simultaneously at maximum power. This means that the available power of the driving motor cannot be optimally utilized. It is, of course, a disadvantage that the pumps for reasons of safety have to be dimensioned to be able to meet with a situation that arises relatively seldom, and it has long been desired that it should be possible automatically to limit the power output of the pumps so that the sum of the maximum power output may safely exceed that of the driving motor. In this manner, it would be possible to run one or more--but not all--of the pumps at maximum power, and as soon as the total power output approaches the available power output of the driving motor, the power output would be reduced to a value immediately below the available power output, without incurring the risk of overloading.